1. Field of the Invention
This invention relates generally to refrigerating apparatus and more particularly, it relates to refrigerant expansion valves for controlling the flow of liquid refrigerant from the condenser to the evaporator. The invention has particular applications in certain automotive air conditioning systems utilizing a constant displacement compressor.
2. Description of the Prior Art
In U.S. Pat. No. 3,803,864 issued to K. W. Cooper on Apr. 16, 1974 and assigned to the same assignee, there is disclosed an expansion device which includes a pair of springs acting against the opposite sides of a diaphragm for controlling the movement of a valve member.
In U.S. Pat. No. 3,034,534 to E. B. Gustafsson issued on May 15, 1962, there is disclosed an expansion valve which includes an externally controllable valve for regulating the pressure between a pair of chambers in order to suppress oscillations in the valve.
In U.S. Pat. No. 2,579,334 issued to N. Plank on Dec. 18, 1951, there is described a pressure-responsive flow regulator which includes a damping device consisting of a pair of flexible diaphragms disposed within a housing to form two pressure chambers on each side of the respective diaphragms. A spring cooperatively engages one of the diaphragms for actuating a valve member.
As is generally well-known in the art, a thermostatic expansion valve is commonly utilized in a refrigerating apparatus for maintaining a constant superheat of the gaseous vapor exiting the evaporator. However, a refrigerating apparatus which includes such a combination of an expansion valve and an evaporator is rarely in a stable condition as oscillation in the valve-evaporator control loop operation usually appear due to an excess of gain or phase in either the valve or the evaporator transfer function. Thus, it would be desirable to provide a thermostatic expansion valve having compensation means such as a mechanical lead-leg structure to compensate for any time delay in either the operation of a valve member or in the evaporator flow-to-superheat transfer relation. In view of this improved expansion valve construction, wide fluctuations or oscillations in the operation of the valve-evaporator control loop are prevented.